In recent years, for clinical application of a monoclonal antibody, a therapy with administration of a monoclonal antibody preparation has been developed. A monoclonal antibody preparation may effectively be used through interaction between a monoclonal antibody and an antigen occurring within the living body. Thus, efficacy of a monoclonal antibody preparation may be enhanced if an expression level of said antigen is previously tested to select subjects to be applied with said preparation. A monoclonal antibody may be advantageous from the viewpoint of safety and efficacy due to its extremely high specificity. However, in case that diversity occurs in an amino acid sequence of an antigenic epitope region, a monoclonal antibody will become less reactive with an antigen and hence its effectiveness may be deteriorated. Therefore, for use of a monoclonal antibody preparation as a medicament, it will be a useful means for enhancing efficacy of said monoclonal antibody preparation not only to test previously an expression level of an antigen within the living body but also to confirm diversity of an antigen and to select subjects for administration.
Among monoclonal antibody preparations wherein subjects to be administered therewith are tested and selected is anti-HER2 monoclonal antibody (Trastuzumab) now commercially available. Trastuzumab is a monoclonal antibody to HER2 protein that is overexpressed in about 20 to 30% of breast cancer patients. For clinical test for selecting subjects to be administered with anti-HER2 monoclonal antibody, Southern blot or Furuorescent in situ hybridization (FISH) technique for DNA amplification of HER2/neu gene; Northern blot or reverse transcription polymerase chain reaction (RT-PCR) technique for screening overexpression of HER2 mRNA; or Western blot, ELISA or immunohistochemistry technique for screening overexpression of HER2 protein have been attempted. With these tests, efficacy of Trastuzumab has been enhanced in cases of HER2 overexpression, suggesting that in therapy with a monoclonal antibody preparation selecting previously subjects to be administered with said preparation is useful for enhancing efficacy of the monoclonal antibody preparation (e.g. Nippon Rinsho, Vol. 60, No. 3 (2002)).